Some, like credit cards and other financial products, are especially bad since the payments per conversion (i.e. person who looks at the review site and then signs up for the credit card) can be massive. But even seemingly innocent niche markets, like light-weight backpacking equipment, can be full of affiliate marketing.
That said, just because a blog or website is influenced by affiliate marketing doesn't mean they don't have useful information in their reviews. They usually are accurate when describing a product's basic attributes. Where they typically bend the truth is when they're comparing products against each other (the one with higher affiliate payments is almost always better), or they simply won't talk about genuinely better products that don't pay for conversions.